An Instrumental Twist
by thatawkwardfangirll
Summary: Jess just moved to Brooklyn, New York. She's a Shadowhunter looking for friends. One day she goes to visit the New York Institute and meets some kids her age - with one that looks exactly like her. What will happen? How will Clary react? Who will betray and who will be together forever? Read and review! Rated T for language, implications, and some intense scenes.
1. Chapter 1

I hadn't quite come to terms with what I was yet. I knew this was normal to some people, and other would have a heart attack or literally laugh in your face if you tried to explain, but here, where I am, it' absolutely normal. One hundred percent. Did I mention that I'm a Shadowhunter? I've lived in Idris since I was born and two months ago my dad got orders to run to Brooklyn Institute in New York.

New York was beautiful. It wasn't like something you'd see in a book, like Idris, but beautiful as in big city, big lights, big, well, everything. To most people, like me, big is beautiful when you don't look close. The closer you look, the less you see.

In "the big apple", we've had some good times. Yes, I had a little adjusting to do with the slang and the people and the place, but I like it. It gives me a sense of adventure. God knows I didn't need more of _that_.

I'm Jess. I'm 17. I'm a Shadowhunter. And I am the Underdog.

The Shadowhunter world has been going crazy what with all the insane stuff going on in the New York Institute not too far away. I've never really gotten into all the fighting and war stuff in this world I live in. I'm more of a "learn but not do" kind of person. But I do love an adventure. Dad had finally said that I could go visit the New York Institute. I can't wait, to be honest. He said there'd be some kids my age. I honestly haven't seen many Shadowhunter kids my age since Idris. Even then, I didn't talk to many people. But maybe I'll click with them. I need to click with them.

That morning I got on the subway to New York, New York. I smiled remembering the first time my dad had used a subway. He had been all wide-eyed. He was kind of scared and kind of interested. Trust me, the face you make when you're concentrated on those two emotions is hilarious. Take from someone whose had a front row experience.

As I stood on the front step of the Institute, looking around at how ridiculously similar it looked to my Institute, I felt kind of nervous. Yes, Shadowhunters can get nervous. I bit my lip and told myself to suck it up. It's okay.

As cleshe as it is, I knocked. And someone answered. A petite, but fiery girl with red hair and eyes to die for opened the door. "Who are you?" The thing is, she looked exactly like me.

**Author's note: Yeah, hi. Sorry this chapter was short. I don't have much time on the computer... Plus, I thought this chapter should be short just because it's kind of explaining what's happening or whatever. Also, all the characters and places or whatever are copyrighted to Cassandra Clare. The plot was just my idea, although it will have some of the original plot from her story. Please review and comment!**


	2. Chapter 2

It was the weirdest thing in the world. This girl looked _exactly_ like me. I was tempted to do that whole thing where you like lift each hand up and see if they did the same, sort of like a mirror image, but I didn't. Pfft, that'd be totally unprofessional.

"Um... Whoa," I breathed out. Yep, that's me, totally professional. She hesitated, seemingly as shocked as I was about the whole thing, then called out, "Jace!" Jace? Where had I heard that name before? I pondered it before I saw a guy, maybe 17, come to the doorway. Did I mention that he was gorgeous? "Yeah, Clar-Whoa. What the..?" She nodded, "Yeah." I was kind of amazed at the way her voice sounded exactly like mine. "It seems we have more to talk about than I had thought... Can I come in?" They nodded and held the doorway open for me.

Stepping in, I saw that not only did it look like my Institute from the outside, but it also did on the inside. The familiar wall colors, hallways, I even caught a peek of a room, which also looked the same. I'm pretty sure I could navigate my way through here and this was my first time to even step in the place. Looking around, even though it was unnecessary, I pushed my big clump of red hair behind my ear. I noticed my...twin?..do the same. We both blushed and looked down. Jace noticed and looked worried. "Alec," he called out,"We may have a problem."

Through the next few minutes, I learned that my twin's name was Clary. They learned who I was, plus, I met Alec, Isabelle, and Simon. They weren't exactly friendly at first, but we got acquainted quickly. It all went uphill after I said that I was Shadowhunter. It seemed to make them believe me.

"Well, just to let you know, I had know idea we...looked the same... I live in the Brooklyn Institute and was looking to make friends here. I didn't know...yeah." They all looked around at me. It was kind of sad that all the guys were like ridiculously gorgeous. Especially Jace. I noticed that he and Clary seemed close, so I assumed they were dating. Looks like I got the bad end of the twin stick.

Anyways, onto non-love related problems. They explained everything about what had been going on here in New York. That's when I realized where I knew Jace. I had seen him in Idris at a small bookstore. I didn't mention anything because it really wasn't that big a deal. We all chatted for a minute, obviously trying to avoid the fact that two of us looked exactly the same. I bet I could get away with a lot if..maybe.. No, never mind. I want to make friends. Blaming bad things on my twin wouldn't exactly help that.

"Is there someone who runs this Institute? Maybe they could explain this...whatever this is, anyway." I said cautiously, not really sure what I was 'allowed' to say. "Alec and Isabelle's mom runs it. I don't think they can help us with this.., but there might be someone who can," replied Clary. "Who?" I asked. She stood up (and looked very awesome doing it, if I do say so myself) and said, "My mom."

The next few minutes were all a blur. It was almost like we were going into battle, but we weren't. Everyone explained to me about how Clary's mom looked almost exactly like her, as mom's usually do, so, of course, it definitely was her mom. Clary said she had a brother, but you could tell it was a...touchy subject. She muttered something about her mom already lying to her enough, but I was secretly hoping that maybe we were related. Maybe I would finally have a sibling.. Finally.

Biting her lip, they arrived at a small house in downtown New York. It looked like it was a sort of a bookstore. Anyways, we walked inside and Clary called out, "Mom!" I heard a female voice come from a room to the right, "Oh! Clary, I wasn't expecting you to come to-" She arrived into the current room we were in, maybe the living room, and stopped like a deer in headlights. She looked from me to Clary then back again. "What? I...What?" she said, clearly confused, shocked, and maybe even a little scared.

Clary said, "Mom? Do you have an answer to this?"

"I..," she stammered, "This wasn't supposed to happen." She ran her hands through her hair and started pacing back and forth. "Mom?" Clary half shouted, half whispered, "Mom, what're you talking about?"

Her eyes were practically bugging out of her eyes, and, by everyone's expressions, she didn't normally do this. "Look, now that you know I have twins, you may be in danger. Listen, Jonathan will come for you, whether it be my Clary or, what was your name? Jess? I'm pretty sure that's what I told them to name you. Anyways, he'll come. But, here's the thing. You are half sisters. You may look exactly alike and may be the same age, but you do not have the same father. I know this is crazy and I know you're scared, but you must go now. Go to Idris. Now. Save yourselves." She quickly backed away.

I had imagined meeting my birth mother for years. I never once thought that would happen. She looked like a raging lunatic! I wanted to be mad, but I couldn't. Fear is overriding any emotion I could've had at that moment. Who is Jonathan? Why would he be coming for me or for Clary? What was this whole thing about my birth father? I had so many questions and turned to Clary and asked the most stupid one, "What do we do now?" She turned to me with her jaw set, "We run."


	3. Chapter 3

Once again it was a blur as we prepared for actual battle, sort of. It was crazy but calm. There was a dangerous aura around the New York Institute as we prepared to go to Idris. We all went to explain to the Lightwood's mom, Maryse, what was happening. She looked like a bitter woman to me, but ended up being okay with us going, telling us to be safe. As if we weren't gonna try.

Although I had more questions than my brain could hold at the moment, I still moved swiftly and quietly as a proper Shadowhunter should, but something tells me that my life isn't exactly going to be 'proper' anymore. The way things were being ran around here had me a little confused, but I could handle it. 'Wait, guys! What about my family? They're still in Brooklyn! They're gonna be looking for me!" I said, panicked. Okay, so maybe I couldn't handle all of it. "Don't worry," Alec replied, "I'll get Magnus to send them a fire message, so they won't worry too much. I mean, they'll worry, but not too much. You are a Shadowhunter after all." I nodded, calming down.

Everyone had bags packed, and Clary held one out to me, "I had too many clothes anyway. Plus, something tells me that you're my size." She smiled and I laughed at the corny joke. Grabbing the bag, I slung it over my shoulder.

"So where are we going in Idris? I mean, if we're running from someone, it's not like we can stay in a house, can we?" Everyone seemed to look at each other then back at me. "That's the one question that we can't answer," replied Jace, always quick to say something. Are these guys serious? We're going into Idris, running from who-knows-what, and they have no idea where we're gonna stay?!

Like I told you from the beginning, I'm not much of a Shadowhunter. I like things organized and planned ahead. This...this is not what I'm used to, but I set my jaw, stood a little straighter, and nodded, "Let's do this."

I walked confidently towards the door and stopped in my tracks when I heard someone clear their throat. "Jess?" said Clary, clearly containing a giggle. "Yes?" I asked, confused. "That's the wrong door.." she answered. I looked back at the door that I had been headed for and saw that, indeed, it had been the wrong door. Just a feeble mistake! I blushed slightly and said, "Maybe you should lead the way." She nodded and smiled, then headed in the opposite direction.

As I walked beside Clary down the long, twisted corridors of the Institute, I finally whispered to her, "So who is Jonathan?" Her whole body went tense then back to relaxed in a millisecond. "He's my brother. Jonathan is his birth name. We all call him Sebastian. It's a long story. I'll tell you about it when we get to Idris." I could tell that she didn't want to tell me, but she would. And I liked that.

We had just walked out of the door and I was gonna ask another question when all of a sudden, a seraph blade flew through the air, right past my ear. A boy, maybe a little older than all of us appeared out of the shadows. "Hello, sister. I see you've met Jess," he said. "Sebastian?" I asked. What was he doing here? Why did he dye his hair? I looked back and forth from Clary to Sebastian. "Do you two know each other?" I asked, nervous and confused. "Oh, yes, Jess. Very well, actually." What? If it was even possible, I was more confused that before. "Sebby, stop talking nonsense," I said, walking towards him, "What is up with you? I told you that I had to move to New York because my parents got the job for the Institute in Brooklyn! Did you follow me here?" I looked up at him, at the familiar lines of his face and the color of his eyes, the pale color of his skin... I just had to hug him. I reached my arms around him and hugged him tightly, his scent overflowing around me. "Derek, just tell them that you're messing with them and I'll take you back to Idris, okay?" I said, trying to get him to look at me, but his eyes were set on the group behind us.

"Jess," he whispered quietly, but barely loud enough to where the others' keen Shadowhunter ears could hear, "I'm sorry that you had to know this now. I had hoped that you wouldn't have met them, that you wouldn't be here on the edge of betrayal, but you are. I want you to know that no matter what they tell you about me, you will always be my love and my weakness." My heart was thumping out of my chest at the look he was giving me and I lost it, leaning up and kissing him, putting all my love and thoughts into it so he knew how much I loved him. I pulled back and wiped a few remaining tears from my eyes. "Seb, look at me. D-Don't do this. It's okay. We're okay," I said, stuttering, trying to not only convince him, but also me.

As hard as I tried to keep him from doing so, he pulled away, looking out at the people that had watched the whole encounter with shocked expressions. Jace looked like his eyes were about to pop out of his head and Clary looked like she was gonna be sick. "Guys, he's not bad. I don't know what you've hear about him, but-" I started, but quickly got interrupted by Clary, who said, "Jess, get away from him now." She tensed up, obviously getting ready for a battle that didn't seem necessary to me. "But why-" I started again. "_Get away." _she practically growled at me. Sebastian said, "Go, Jess, and remember what I said." And, with a last look at everyone, he vanished on the spot. Well, that was new.

Jace looked back and forth fro me to Clary then said, "So _that's_ what it would look like if Clary and Sebastian kissed. I've always wondered."

Clary and I, at the same time, said, "Shut up, Jace!"

**Author's note: So what do you think so far? Getting them plot twists muahahahahaha. Please review and follow or whatever, that'd be great! Feel free to PM me some ideas or your input, that'd be great! Thanks, and see you next time.**


	4. Chapter 4

After that...emotional... moment, Clary seemed to clear her head then become all business. I don't know if I liked her that way or not. Jace seemed to think that it was "sexy," though. Pervert.

We continued our journey to Alec's boyfriend's house, Magnus, I think his name was. Did I mention he's a warlock? Well, he is. I tried not to judge because I, personally, love gay guys, but a _warlock?_ This guy better be gorgeous. Anyways, when we got to his house, Magnus made a portal that went straight to Idris. The Clave must've given him special permission. Impressive.

Like every other warlock, Magnus had one feature that made him look different. He had cat eyes, dangerous, but gorgeous. Alec and Magnus shared a chaste kiss and then Magnus made the portal, in which we stepped through with ease.

On the other side of swirling blackness was Idris, my home. I grew up here. I knew every street and every house and every person. I looked at where we had landed and saw that it was just on the outskirts of the city. I looked around, breathing in the familiar, yet foreign, air.

We stepped through the gates of Idris and I looked around, seeing the cobblestone sidewalks and the newly-carved benches. I looked at a slightly older bench outside the bookstore where Jace and I met and my heart swelled.

_"Sebstian!" I whispered, peeping around the corner, nervous about getting caught for being out so late. _

_"You rang?" he breathed onto my neck behind me, causing me to shiver involuntarily. I remembered other things that he had done with that mouth, that oh so perfect mouth... I quickly blinked, moving onto other thoughts before I got caught up in it. _

_I closed my eyes for a moment then turned around to look at him. "Are you happy? I'm here. After what you did to me, I don't know why I even bothered," I said icily, referring to me finding Sebastian kissing my best friend at _our_ spot just days before, "So what do you want? Here to gloat?" I had said it harsh, but on the inside I was breaking, crushed and hurt._

_He looked down at me, his eyes unreadable and dark, dangerous. He reached his right hand out, caressing my face for a moment before I quickly flinched away from him as if stung with a thousand volts of electricity. "Don't touch me," I practically growled at him. "Jess..," he said slowly, "it was nothing. She was nothing. We aren't even dating! You told me you wanted to see other people!" I shook my head. I had said that, but I hadn't meant that. He had been boasting, once again, about how fun it was to kill people and I snapped and said something that I didn't mean. And he knew it. _

_"Is that what you wanted to tell me? Because you know what, Sebastian? I'm hurt. I'm just plain done with what you keep doing to me over and over. I had hoped that maybe you would try to apologize or something, but I guess not. So, this is goodbye forever," I said, pulling out a seraph blade and, before Sebastian could do anything, I plunged it into my stomach, falling to the ground. _

I was brought back to reality by Jace waving his hand in my face. "Jess?" he said, "Where is the mansion?" I held my hands to my stomach, feeling sick, and waited until it passed."Oh, um, this way," I answered, taking them through the trail that I had made in the woods leading to the mansion where I had spent a week crying until Sebastian had found me. I shook the memory away as we arrived.

"Welcome to Casa de Shadowhunter."

Simon snorted and I rolled my eyes, leading the way in. Everyone looked around, fascinated. Except Jace, of course, he had to keep up the arrogant act that he had worked so hard on.

"Make yourselves comfortable. If you're a, uh, couple then you can share a room. Just...keep it down," I mumbled quietly, but loud enough where everyone could hear me. Clary blushed and Jace smirked down at her. While they were obviously undecided, Isabelle immediately grabbed Simon's arm and dragged him up the stairs. I'm pretty sure I heard her say, "...let's see how fast you can really move..." I fought down the urge to throw up. Meanwhile, Alec and Magnus had pretty much the same reaction as Clary and Jace. Alec blushed and Magnus smirked at him.

When everyone got settled in their rooms, I walked outside, pulling my jacket closer to me in the cold. I sat down on the log, thinking about Sebastian and what lies ahead for us.

After staying out there for awhile, I heard Clary and Jace fighting. I sighed. _Young love_, I thought to myself. I heard a door slam and a huff. That was Clary. I'm pretty sure she went in the basement to cool off. Twenty minutes after that, I saw Jace at the door. He looked around and saw me, running up to me in relief.

"Oh God," he said, running up to me and pulling me into a hug. I realized that he thought I was Clary and I tried to say, "Jace-" He shook his head, cutting me off and saying, "I'm so sorry that I pushed you and yelled at you. I shouldn't have." He leaned down swiftly and kissed me passionately. I froze with his lips still on mine. I pushed him away, holding my hand to my lips. "Jace, I'm Jess!" I yelled, completely flustered and confused. There was a moment where he just looked at me in confusion and then realized what had just happened.

"Oh, no. Oh no, oh no, oh no," he muttered to himself, pacing back and forth and running his hand through his perfectly blonde hair, "I've gotta go tell her. I didn't mean to! I just, I thought you were her and I just had to..."

I quickly shook my head. "No. You can't tell her. What she doesn't know won't kill her," I said, looking up at his gorgeous face. He slowly nodded and then walked back inside, glancing back at me.

I walked a little ways away from the house and then took the note out of my pocket that Sebastian had secretly slipped into my pocket. I opened it and it read:

_You know I love you. Come to the cave and I'll show you that you won't forget it._

_ -Sebastian_

I paused for a moment, unsure what he had in store, but pushed it aside and started walking to the cave. Everyone deserves a second chance.


End file.
